Near-IR tunable laser with an integrated LiTaO3 electro-optic deflector

We report the successful demonstration of a near-IR tunable laser (1525.4-1558.2 nm) that uses an integrated LiTaO3 deflector in combination with a reflection grating as an electronically tunable filter. The electro-optic deflector is a unique integrated optical device and consists of a horn-shaped array of electro-optic prisms in series. The almost 33 nm of tuning covers a wavelength region of high interest to the communications industry (1527-1550 nm).     

Integrated high-power electro-optic lens and large-angle deflector

We present a theoretical discussion and experimental demonstration of what to our knowledge is a novel integrated electro-optic lens and beam deflector fabricated in lithium tantalate. The cylindrical lens collimates Gaussian beams as small as 4 mum in diameter, whereas the independently controlled deflector is capable of scanning the collimated beam through an angular range of nearly 20 degrees .     

Domain-engineered lithium niobate as a medium for an integrated solid-state two-dimensional color laser scanning system

A recently proposed alternative to conventional prism-type electro-optic solid-state deflectors is the single interface deflector. Whereas these deflectors are comparable in performance to prism-type deflectors, they are far simpler in construction. This simplicity obviously has the advantages that it reduces fabrication time and cost and allows for easier optimization. Less obviously, but more advantageously, the simplified geometry provides, for the first time to our knowledge, the ability to achieve a completely solid-state two-dimensional beam deflector. We also detail how the two-dimensional deflector can be further augmented by the addition of intensity and color switching to the device.     

Resolution considerations in electro-optic, single interface deflectors

We discuss the maximum theoretical resolution of a single interface, electro-optically controllable beam deflector in domain-engineered LiNbO3 and report on experimental results for implementation of devices optimized either for maximum resolution or for maximum deflection angle. For the resolution optimized device we observed approximately 50 resolvable spots for a +/- 1250-V range, which to our knowledge is a report of one of the highest ratios of resolution per volt from a solid-state electro-optic beam deflector.     

电光晶体研究进展

电光效应就是晶体折射率随外加电场而发生变化的现象。这种效应在光调制领域中有广泛的应用,可以制作激光器件,如高速电光开关、电光偏转器等。介绍了电光晶体的类型,以及电光晶体的研究现状和发展趋势。比较详细地介绍了偏硼酸钡晶体(1985年由我国科学家发现的第一个"中国牌"晶体)、磷酸钛氧钾和磷酸钛氧铷晶体、硅酸镓镧晶体等的特性和应用。最后提出了有关电光晶体研究的建议和展望,指出,必须从理论和实际两个方面来开展对电光晶体的研究,争取有所突破。     

Tuning of a Ti3+:sapphire laser by an electro-optic beam deflection method

A wavelength-switching method for tuning a self-injection-seeded Ti3+:sapphire laser that uses an electro-optic beam deflection technique is reported. A LiNbO3 prism was employed in a tuning arm of the dual-cavity Ti3+:sapphire laser, and wavelength tuning of approximately 94 pm was attained by altering the deflection angle with the application of an electric field of 10 kV/cm to the prism. The spectral characteristics of the output laser were mainly determined by the diffraction grating in the dual-cavity laser, and the electro-optic prism just behaved as a light-beam deflector for the wavelength tuning purpose. This configuration can allow a simple tuning approach where fast and stable electronic wavelength switching is required in a narrow tuning range, on an order between a few tens of picometers to nanometers, without involving any mechanical movement.     

Advanced Optical Techniques

The development of a digital electro-optic light beam deflector (DLD) is described. Each deflection stage consists of a DKDP polarization switch with a coating of transparent electrodes (longitudinal electro-optic effect) and a calcite prism for angular deflection. Effects which limit the switching frequency and the capacity speed product (i.e. product of the number of resolvable beam directions and the switching frequency) are theoretically investigated. A four-stage solid-state DLD has been realized which operates at switching frequencies up to 10 kHz and at a random access time of 30 μ s. The system is going to be expanded to 8 × 8 stages for the addressing of 256 × 256 beam directions.     

Large-angle electro-optic laser scanner on LiTaO(3) fabricated by in situ monitoring of ferroelectric-domain micropatterning

We report on a horn-shaped electro-optic scanner based on a ferroelectric LiTaO(3) wafer that is capable of scanning 632.8-nm light by an unprecedented 14.88 degrees angle for extraordinary polarized light and by 4.05 degrees for ordinary polarized light. The device concept is based on micropatterning ferroelectric domains in the shape of a series of optimized prisms whose refractive index is electric field tunable through the electro-optic effect. We demonstrate what we believe is a novel technique of using electro-optic imaging microscopy for in situ monitoring of the process of domain micropatterning during device fabrication, thus eliminating imperfect process control based on ex situ monitoring of transient currents.     

Diffraction from tunable periodic structures: application for the determination of electro-optic coefficients

We discuss a method for measuring electro-optic coefficients by measuring diffraction from a tunable grating. The method involves measuring the changes in the diffraction pattern of a reflection grating, where applied electric fields of alternating direction induce changes in the index of refraction through the electro-optic effect. For certain geometries, these applied fields cause period-doubling effects that produce new peaks in the diffraction pattern. Numerically calculated diffraction patterns are presented for the assumptions of both homogeneous and inhomogeneous fields. Peak splitting, as a function of both the number of slits illuminated and the induced change in the index of refraction, is observed and discussed. Finally, the usefulness of our method for the measurement of electro-optic coefficients is discussed.     

Bulk electro-optic deflector-based switches

We propose two novel electro-optic (EO) deflectors based on two new nonrectangular geometries: the parabolic and the half-horn configurations. These devices not only provide excellent deflection angles, but also have the potential to build nonblocking 2 x 2 optical switches. A deflector figure of merit is defined, and comparisons with existing EO deflectors are given. Devices fabricated in LiTaO(3) demonstrate 3 dB of average insertion loss and 3 degrees deflection angles. These results represent the best deflection performances to our knowledge reported to date for bulk EO deflectors.     

Tunable power splitter based on an electro-optic multimode interference device

Power splitters based on multimode interference (MMI) devices that offer the possibility of dynamically tuning the power-splitting ratio using electro-optic (EO) polymers are presented. The so-called 1 x 2 electro-optic MMI (EO-MMI) is demonstrated to provide a tuning range of 6 dB at approximately 54 V as theoretically predicted. Also a method is discussed to reduce the driving voltage by generating multiple beats, which provide 15 V for a tunable range of 10 dB for r(33)=15 pm/V at wavelength 1.55 microm.     

Guided wave acousto-optic and electro-optic tunable filter designs with relaxed beam-splitter requirements

New designs for acousto-optic tunable filters and electro-optic tunable filters with the Mach-Zehnder configuration are proposed. The new designs differ from conventional designs in three respects: (1) polarizing beam splitters are not required, (2) the optical path difference for the waveguides between the beam splitters is a half-wavelength, and (3) the relative positions of the polarization coupling regions in the two waveguides are displaced in the propagation direction by half of the spatial period of the perturbation responsible for the coupling. Because the new designs provide an additional degree of freedom in achieving the required beam-splitter performance, they are expected to be much easier to fabricate than conventional filter designs with polarizing beam splitters.     

C-band external-cavity wavelength-tunable laser based on a liquid-crystal deflector

A novel C-band external-cavity wavelength-tunable laser is proposed. The laser consists of a semiconductor gain chip, a collimating lens, a fixed etalon, a liquid-crystal deflector and a diffraction grating in a Littrow configuration. The lasing wavelength of this tunable external-cavity laser can be tuned to 19 wavelength channels of 100 GHz spacing. All channels are within 2.5 GHz of the ITU grids with a side-mode suppression ratio of approximately 35 dB over the whole range.     

Numerical analysis of a high-resolution fast tunable filter based on an intracavity Bragg grating

A fast tunable filtering technique is proposed associating a diffraction grating with an intracavity Bragg grating. The bandwidth and the tuning range of this filter can be easily adapted by changing the diffraction grating's orientation, or its period, and its response is uniform over the whole tuning range. A numerical simulation of the filter response to a Gaussian beam has been developed, and it fits the experimental results allowing a calculation of the performances that could be obtained with more specific elements. For example, using a commercial acousto-optic deflector would allow a separation of 500 frequencies. It would then be possible to have a tuning range of 100 nm with a bandwidth of 0.2 nm for optical telecommunications.     

Simulation of cross-talk reduction in multimode waveguide-based micro-optical switching systems by use of single-mode filters

We propose a method to reduce cross talk by using single-mode filters, namely, extracting the fundamental mode from a multimode optical network (EFMON). The EFMON effect is evaluated for a three-step switching system consisting of cascade electro-optic (EO) waveguide prism deflector (WPD) micro-optical switches (MOSs) and a multimode waveguide network. The WPD MOS is optimized for single-mode operation in lead lanthanum zirconate titanate thin films as EO slab waveguides with a driving voltage of 12 V, a length of 310 microm, and a channel distance of 20 microm. Beam propagation method simulation reveals that mode disturbance, higher-order modes, and cross talk are accumulated by switching steps. A single-mode filter for EFMON in the output region of the switching system reduces cross talk to below -20 dB at a propagation length of 2000 microm in the single-mode filter and below -30 dB at 20000 microm.     

Interferometric optical switch enhanced by a multi-resonance ring resonator structure

We propose a novel configuration for optical switches by the use of two coupled ring resonators acting as a phase-shifting element in a Mach–Zehnder interferometer. Because the ring structure is multi-resonant within one period of its phase response, light at any frequency within the period can be addressed by tuning the device across a small frequency interval. This enables the use of low voltages for electro-optic control of the switch, allowing for a tunable photonic switching device that operates at 1?V voltage levels.     

Analysis and Design of a Flat Transducer Array Acousto-optic Deflector with Respect to the Second-order Diffraction

The diffraction of light by an acoustic wave generated by an oppositely phased transducer array is studied. Special attention is paid to the parasitic second-order diffraction which takes place in the usual deflector design at the frequency-band centre, and which results in a decrease in the first-order diffraction efficiency. On the basis of a simplified three-coupled-wave analysis, a modified deflector design is suggested which minimizes the diffraction efficiency dip in the deflector frequency-band centre.     

Polarization dependence of the coupling ratio in LiTaO3 directional couplers

The effect of design and fabrication parameters on the polarization dependence of the splitting ratio in directional couplers produced in LiTaO3 by Zn diffusion has been investigated experimentally at a wavelength of 1558 nm. The directional couplers featured various combinations of waveguide width, separation gaps between waveguides, bending angle, and diffusion conditions. In each case the coupling region was 3.5 mm long. Of particular interest was the identification of parameter sets for which the sum of power splitting ratios from TE and TM inputs equals unity at the output, as needed for electro-optic tunable filters with relaxed beam-splitter requirements.     

分流板开孔面积对微通道平行流蒸发器性能的影响

采用数值模拟与实验研究相结合的方法,以R134a为工质,研究了微通道平行流蒸发器内入口处分流板的开孔面积变化时,对蒸发器的流动和换热性能的影响。结果表明:随着分流板上的开孔孔径增大,蒸发器内的流动阻力会降低,制冷剂流量分配的均匀性变差,而制冷量却先增加后减小。分流板的开孔孔径存在一个最佳值,此时蒸发器内的阻力损失低,制冷剂的流量分配均匀性好,两者的匹配性最好,使得蒸发器的制冷量达到最大。此蒸发器中入口分流板的最佳开孔面积约为150.7 mm2。